Frequently, access to electronic information stored on storage devices is managed through a file system. Often, the stored information is physically or logically divided into blocks. For example, a storage device may logically divide data into 1K blocks. Thus, a file that includes 2K bytes may include a first block of data corresponds to the address range 0 to 1023, and a second block of data corresponds to the address range 1024-2047.
When clients access data managed by a file system, I/O requests are sent to the file system to perform the I/O operations. The data that is specified, by the client, as the target of a requested I/O operation is referred to herein as the “target chunk”. When the boundaries of the target chunk coincide with the boundaries of the blocks that contain the target chunk, then the I/O operation is referred to as an “aligned” I/O operation. On the other hand, if the boundaries of the target chunk do not coincide with the boundaries of the blocks that contain the target chunk, then the I/O operation is referred to as an “unaligned” I/O operation.
Frequently, storage devices and/or file systems are designed to perform aligned I/O operations more efficient than unaligned I/O operations. Consequently, retrieving an entire block may be more efficiently than retrieving a target chunk that is only a subset of the block. Similarly, retrieving two blocks may be more efficient than retrieving a target chunk that spans but does not fully include the two blocks.
Unfortunately, the I/O operations required by clients are not always aligned, and it would place an undue burden on client developers to require clients to be designed to only request aligned I/O operations.
Other types of inefficiencies may occur if I/O operations are not managed intelligently. For example, if the read requests issued to the file system by one application are not coordinated with the read requests issued by other applications, then the file system may, for example, have to retrieve to same block many times in succession. In addition, if applications are responsible for directly sending their own read requests to the file system, then the timing of read requests that have deadlines may have to be handled by the applications themselves, making the applications more complex than desired.
The approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section.